1. Field of the Invention
This invention relates generally to shaft seals and particularly concerns a bidirectional shaft seal for preventing static and dynamic leakage irrespective of the direction of shaft rotation.
2. Description of Prior Developments
A leakage problem has long existed in those applications where a seal, such as an oil seal, is required to operate under bidirectional conditions. An example of a bidirectional seal application is an automotive transmission shaft seal where the transmission shaft rotates clockwise and counterclockwise depending on the direction of vehicle travel.
While conventional oil seals have performed satisfactorily under uni-directional conditions, static and dynamic oil leakage has often occurred under bidirectional operation. For example, no seal leakage may occur under strictly clockwise rotation of a shaft, while significant seal leakage may occur under counterclockwise rotation of the same shaft. Although there is no presently confirmed explanation for this phenomenon, it is possible that shaft microfinish may induce a hydrodynamic effect between the shaft and seal. This effect pumps fluids toward the inside of the seal under one direction of shaft rotation and pumps fluid toward the outside of the seal under the opposite direction of shaft rotation, the latter condition often causing a leak.
Dynamic leakage is particularly common when a seal provided with hydrodynamic pumping elements is used in a bidirectional application. Such pumping elements often include spiral flutes machined or coined in the seal lip. When the hydrodynamic seal is applied to a shaft which rotates against the seal lip so as to pump lubricant or fluid past the seal to the environment, a major leakage problem results.
A need therefore exists for a seal which may operate under bidirectional conditions yet which maintains an effective leak-proof seal at all times regardless of the direction of shaft rotation.
A need further exists for a hydrodynamic seal which maintains an effective seal during bidirectional operation.